Synthetic hypoglycemic drugs currently used clinically as therapeutic agents for the treatment of diabetes are sulfonylurea preparations and biguanide preparations. Biguanide preparations, however, are used only in rare cases because of the limitation for their application due to their aptness to cause lactic acidosis. Sulfonylurea preparations, on the other hand, show solid hypoglycemic function and markedly small side effects, but must be used carefully because they sometimes cause hypoglycemia.
A number of studies have been made on the development of hypoglycemic drugs which can be used as substitutes for the sulfonylurea preparations, but with no success in putting them into practical use.
In recent years, insulin sensitivity enhancing agents which exhibit a hypoglycemic function by enhancing insulin sensitivity in peripheral tissues have received increased attention as substitutes for the aforementioned synthetic hypoglycemic drugs.
There are various compounds which have such an insulin sensitivity enhancing function, of which a thiazolidinedione compound disclosed in U.S. Pat. No. 5,063,240 and represented by the following formula is known as a bisheterocyclic type compound. ##STR2## (See the above patent for the definition of each symbol in this formula.)